Sensitivity to Visual Gain Modulation in Head-Mounted Displays Depends on Fixation
AuthorMoroz, Matthew John
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A primary cause of simulator sickness in head-mounted displays (HMDs) is conflictbetween the visual scene displayed to the user and the visual scene expected by the brainwhen the user’s head is in motion. Agreement between visual scene motion and headmotion can be quantified based on their ratio which we refer to as visual gain. We suggestthat it is useful to measure perceptual sensitivity to visual gain modulation in HMDs (i.e.deviation from gain=1) because conditions that minimize this sensitivity may prove lesslikely to elicit simulator sickness. In prior research, we measured sensitivity to visual gainmodulation during slow, passive, full-body yaw rotations and observed that sensitivity wasreduced when subjects fixated a head-fixed target compared with when they fixated a scenefixedtarget. In the current study, we investigated whether this pattern of results persistswhen 1) movements are faster, active head turns, and 2) visual stimuli are presented on anHMD rather than on a monitor. Subjects wore an Oculus Rift CV1 HMD and viewed a 3Dscene of white points on a black background. On each trial, subjects moved their head froma central position to face a 15 deg eccentric target. During the head movement they fixated apoint that was either head-fixed or scene-fixed, depending on condition. They then reportedif the gain applied to the visual scene motion was too fast or too slow. Gain on subsequenttrials was modulated according to a staircase procedure to find the gain change that wasjust noticeable. Sensitivity to gain modulation during active head movement was reducedduring head-fixed fixation, similar to what we observed during passive whole-body rotation.Additionally, conflict detection seems to be significantly improved with higher peak velocityof head rotation. We conclude that fixation of a head-fixed target is an effective way toreduce sensitivity to visual gain modulation in HMDs, and may also be an effective strategyto reduce susceptibility to simulator sickness.